KR19980024413A - Polyvinyl alcohol composition - Google Patents

Abstract

A polyvinyl alcohol (PVA) composition (I) in the form of an aqueous solution containing (a) PVA, (b) at least one poly-aldehyde with at least 3 carbon atoms, completely masked as a water-soluble hydrogen-sulphite adduct and (c) at least one compound with an acid reaction in water. Also claimed are (i) processes for the production of (I), (ii) a homogeneous, solid, water-soluble PVA pre-mix containing components (a) and (b), and (iii) a process for the production of this pre-mix by mixing water-soluble PVA granules with an aqueous solution of component (b) and then drying the mixture.

Description

Polyvinyl alcohol composition

The present invention provides a self-crosslinking polyvinyl alcohol composition in the form of an aqueous solution that has extended storage stability upon storage, a method for preparing the same, and a sheet and adhesive that is resistant to a film, such as boiling water, that crosslinks at room temperature. to the use thereof for producing a bond).

Adhesives based on polyvinyl alcohol are known in the art. These adhesives can be used in particular in the form of aqueous solutions as raw materials for the attachment of cellulose-based substrates such as wood, paper or cards due to their adhesion. Examples of its application are the production of special paper laminates and helical or parallel sleeves. Polyvinyl is also used as a packaging material with a wide variety of other applications, and this packaging material is used on its own or elsewhere as the laminate component in the composite film.

A known disadvantage of these applications is the hydrophilicity of polyvinyl alcohol, which, when used, causes poor water resistance of the adhesive bond or results in an inappropriate oxygen barrier effect under high gas humidity conditions in the film. By using sufficiently hydrolyzed polyvinyl alcohol that is insoluble in cold water, for example, its use as a paper adhesive results in certain resistance to the action of cold water, but the resistance of the adhesive to boiling water is not achieved or partially soluble in cold water. It does not become a waterproof adhesive film or cast film formed from an aqueous solution that is easy to prepare hydrolyzed polyvinyl alcohol.

In principle, it is known to reduce the water sensitivity of polyvinyl alcohol using as many reagents as possible, for example bifunctional aldehydes. See C. A. Finch in Polyvinyl Alcohol, C. A. Finch (Ed); John Wiley and Sons, New York (1992), Chap. 9].

Boiling water according to U.S. Patent No. 4,376,183 from an aqueous composition comprising polyvinyl alcohol, crosslinkable dialdehyde dissolved in an aqueous form, and a metal orthophosphate, preferably an orthophosphate of aluminum or iron, dispersed in the solution. Polyvinyl alcohol films can be produced that are resistant to and suitable as flexible packaging materials. Resistance to hot water is achieved through subsequent heat treatment.

Japanese Patent Application No. 77-117991 [Chemical Abstracts 88: 74939] discloses a polyvinyl alcohol molding compound that is resistant to boiling water from an aqueous solution by crosslinking with a bifunctional aldehyde having at least 3 carbon atoms in the presence of an acidic catalyst containing salts. It describes the preparation of

Resistance to boiling water of wet spinning polyvinyl alcohol fibers can be achieved by treating the fibers with dialdehydes (e.g. glutaraldehyde) or dialdehydes acetals (e.g. tetramethoxypropane) in a medium acidified with sulfuric acid. It can be improved according to Patent Application No. 93-163609 (Chemical Abstract 119: 141112). The aqueous polyvinyl alcohol solution includes boric acid added before spinning.

Waterproof polyvinyl alcohol compositions suitable for adhesives and sizes are described in Japanese Patent Application No. 94-157860 (Chemical Abstracts 121; 257180). The composition comprises, in addition to polyvinyl alcohol, chitosan, aldehydes such as glyoxal, reducing agents and free radical scavengers such as hydroquinone monomethyl ether. Reducing agent groups include sulfur compounds, in particular alkali sodium hydrogen sulfite.

Although the cited prior art in principle provides access to polyvinyl alcohol films that are resistant to boiling water, the compositions are rapidly to be crosslinked in acidic media by bifunctional aldehydes having at least 3 carbon atoms. It tends to gel and therefore only has limited stability upon storage. This is a particularly detrimental property for use as an adhesive.

It is therefore an object of the present invention to provide a polyvinyl alcohol composition in the form of an aqueous solution which exhibits extended stability upon storage for at least 4 weeks, from which a high level of resistance to boiling water, preferably when dried at room temperature. Films containing can be prepared.

This object is achieved by a polyvinyl alcohol composition in the form of an aqueous solution which, in addition to the polyvinyl alcohol composition, comprises at least two functional aldehydes having at least 3 carbon atoms and completely masked in the form of a water soluble hydrogen sulfite adduct. From the crosslinkable aldehyde groups can be released in a controlled manner.

The present invention provides a polyvinyl alcohol composition in the form of an aqueous solution comprising at least one polyvinyl alcohol, at least 3 polyaldehydes having at least 3 carbon atoms and completely masked as a water soluble hydrogen sulfite adduct and at least one compound acidic in water.

In general, polyvinyl alcohol is prepared by hydrolysis of polyvinyl acetate. Suitable polyvinyl alcohols have a degree of hydrolysis of 70 to 100 mol% and a viscosity of 2 to 70 mPa · s as an aqueous solution at 4% concentration. Polyvinyl alcohols having a degree of hydrolysis of 80 to 98 mol% are used, in particular for their solubility in water. Suitability is imparted, in particular, by partially hydrolyzed polyvinyl alcohol which is soluble in cold water, having a degree of hydrolysis of about 88 mol% and a viscosity of 18 to 40 mPa · s as an aqueous solution at a concentration of 4%.

The concentration of the aqueous solution is at least 0.1% by weight and its upper limit is determined by the molecular weight of the polyvinyl alcohol. It is preferable to operate at a concentration of 2 to 30% by weight depending on the degree of viscosity. It is preferably operated at a concentration of 1 to 25% by weight, particularly preferably at a concentration of 5 to 15% by weight. The viscosity range of the treatment composition after addition of the additives described below is preferably less than 10,000 mPa · s, preferably less than 1,000 mPa · s, in particular less than 500 mPa · s. This viscosity range is achieved within the above-mentioned concentration ranges when polyvinyl alcohol of molecular weight is used which has a viscosity of an aqueous solution of 4% concentration at 20 ° C. of 4 to 30 mPa · s.

Examples of suitable bifunctional or higher aldehydes having at least 3 carbons and completely masked as a hydrogen sulfite adduct and in which crosslinkable aldehyde groups can be released in a controlled manner in an acidic medium are malonaldehyde, succinate, 2- Hydroxysuccinaldehyde, glutaraldehyde, 3-methylglutaraldehyde, 3-hydroxyglutaraldehyde, adialdehyde, 2-hydroxyadiphaldehyde, heptanedial, octanedial, nonanedial, decandial and cis- And derivatives of trans-2-butenedial or polyacrolein and dialdehyde starch. Suitable derivatives of the aldehydes are adducts with alkali metal hydrogen sulfite. Particularly preferred components are glutaraldehyde and succinate aldehydes, in particular glutaraldehyde bis (sodium hydrogen sulfite) and succinate bis (sodium hydrogen sulfite) and adducts of sodium- or potassium hydrogen sulfite. It is of course also possible to use mixtures of other adducts.

The component is used in an amount such that the molar ratio of (nonsulfite adduct to vinyl alcohol) is (0.0001 to 0.5): 1, preferably (0.005 to 0.05): 1.

The acidic compound in the novel polyvinyl alcohol composition is Bronsted acid or Lewis acid. Suitable Bronsted acids are preferably acid salts of boric acid, meta-phosphoric acid, ortho-phosphoric acid or ortho-phosphoric acid. Also examples of Bronsted acids having a suitable pKa value of less than 2.5 are aqueous inorganic acids such as sulfuric acid or hydrochloric acid, or benzenesulfonic acid and p-toluenesulfonic acid. These may be used alone or in combination with the aforementioned acids which exhibit a particular pH. Lewis acids are water-soluble salts of polyvalent cations that are in hydrolysis equilibrium in aqueous solutions, in particular salts of Cr (III), Al (III), Zr (IV) or Fe (III) [e.g. chromium (III), ammonium chloride, Ammonium nitrate, zircon oxychloride or iron (III) chloride]. Of course, mixtures of these compounds can be used.

The amount of acidic compound is an amount that provides a pH of less than 6, in particular less than 4.5, particularly preferably 1 to 3.5, in the polyvinyl alcohol composition. The acidic compound is preferably used in an amount of at least 0.001% by weight, in particular 0.1 to 50% by weight, based on the weight of the polyvinyl alcohol. In addition, it is preferable to use a compound capable of participating in the polyvinyl alcohol in the composite compound. Particular preference is given to using aluminum chloride or aluminum nitrate. The amount of the acidic compound further involved in the polyvinyl alcohol in the composite compound is preferably 5% by weight or more, in particular 10 to 50% by weight, based on the weight of the polyvinyl alcohol.

The present invention also provides

Preparing an aqueous polyvinyl alcohol solution in a desired concentration range,

Provided is a process for preparing a novel polyvinyl alcohol composition in the form of an aqueous solution by mixing an aqueous solution with a polyaldehyde and an acidic compound that is completely masked as a water soluble hydrogen sulfite adduct, preferably by adding an aqueous solution of the components. do. The order of addition is not limited. The solution simultaneously performs crosslinking of the polyvinyl alcohol by hydrolysis of the hydrogen sulfite adduct adjusted as a function of time and binding to acetal and has a sufficiently low pH achievable through the selection of acidic compounds. The pH is less than 6, preferably less than 4.5, in particular less than 3.5.

It is also possible to add at least a stoichiometric amount of alkali hydrogen sulfite, disulfite or pyrosulfite relative to the amount of free aldehyde and the amount of aldehyde present, thereby completely masking the hydrogen sulfite adduct itself in the polyvinyl alcohol solution present. The above aldehyde can be manufactured. This step is performed before adding the acidic compound. Further, other free aldehyde derivatives are initially formed to produce free aldehydes in an acidic medium, preferably below pH 6, and the aldehydes themselves are added to stoichiometric amounts of alkali metal hydrogen sulfides, disulfides or pyrosulfites to form hydrogen sulfites thereof. Can be converted to adducts. Examples of suitable acetals are cyclic acetal 2,5-dimethoxytetrahydrofuran, 2,5-diethoxyhydrofuran, 2,6-dimethoxytetrahydro-2H-pyran and 2,6-diethoxytetrahydro-2H- Piran. Particularly suitable compounds from this group are bisdimethyl- and bisdiethyl acetals of malonaldehyde, succinate aldehyde and glutaraldehyde.

In principle, the hydrogen sulphate in the latter two variants, since the pH-dependent equilibrium between the free aldehyde and its hydrogen sulfite adduct is first added after the salt providing the equilibrium concentration of sulfite ions in an acidic aqueous solution. It is not important whether the formation of the pit adduct is quantitative.

A further aspect of the process for producing novel polyvinyl alcohols which are crosslinked at room temperature and resistant to hot water and intended for the production of adhesives, are in the form of aqueous solutions which retain extended stability upon storage in film production. A uniform, solid, water-soluble polyvinyl alcohol preparative comprising the above aldehyde preliminarily masked as a crosslinking component having at least 3 carbon atoms and completely masked as a hydrogen sulfite adduct and subsequently being converted to an aqueous solution by addition of the acidic compound. Preparing the mixture preferably in the form of storage stable polyvinyl alcohol granules.

The starting material in the preparation of the polyvinyl alcohol premix is in the form of at least partially water soluble powder or granules of polyvinyl alcohol. Suitable diameters of the polyvinyl alcohol granules are preferably 0.1 to 5 mm. These granules are aldehydes having at least 3 carbons which are completely masked as a hydrogen sulfite adduct, preferably in the form of an aqueous solution, using conventional mixing equipment such as, for example, a tumble mixer, a star stirrer or a forced mixer. Mixed with When used, the amount of feed water uses an amount in which the overaldehyde is substantially absorbed by the granules and swells, resulting in a substantially uniform product when the granules are dried. No heat supply is required during mixing operation. During subsequent drying, the temperature should not exceed the thermal decomposition temperature of the aldehyde derivative.

From the polyvinyl alcohol premix in the form of polyvinyl alcohol granules, a homogeneous aqueous solution preliminarily comprising an aldehyde compound masked as hydrogen sulfite can be prepared by a method known per se. The solution can then be mixed with the above acidic compound to obtain a novel aqueous polyvinyl alcohol composition.

In contrast to a simple mixture of anhydrous polyvinyl alcohol granules and finely divided hydrogen sulfite adducts of aldehyde adducts having at least 3 and more than 2 functionalities, the preliminary mixtures in the form of modified polyvinyl alcohol granules are poor, such as high atmospheric humidity. It can be stored for several months even under the storage conditions, so that a uniform aqueous solution can be obtained even after an extended period of time.

Uniform solid water-soluble polyvinyl alcohol premixes and methods for their preparation are provided by the present invention.

The aforementioned novel polyvinyl alcohol compositions in the form of aqueous solutions advantageously produce films and adhesives that are resistant to boiling water without thermal activation and exhibit improved stability upon storage for at least 4 weeks compared to the compositions of the prior art. Further treatment of the resulting film at elevated temperatures can further improve the resistance to boiling water and shorten the drying time.

The following examples are intended to illustrate the present invention. All parts and percentages are by weight unless otherwise noted.

Example

Examples 1-3 and Comparative Examples C1 and C2

100 parts by weight of a 10% aqueous solution of partially hydrolyzed polyvinyl alcohol having a viscosity of 18 mPa · s with a hydrolysis degree of 88 mol% and a 4% aqueous solution at 20 ° C. with stirring, uniform chloride at a concentration of approximately 30% Mix with 3.5 parts of saturated aqueous ammonium solution. Subsequently, the additives listed in Table 1 are stirred and incorporated into the mixture. The solution is used to prepare a cast film having a thickness of about 0.25 mm and dry it for 48 hours at room temperature. Four pieces of about 2 cm × 2 cm in size are taken from each film to determine the fraction insoluble in boiling water. Half is used to determine the content Ts (%) of anhydrous twice (for 6 hours at 120 ° C.). The other half is weighed to (m ₁ , m ₂ ) and treated for 2 hours in boiling water. Subsequently, the fraction insoluble in the boiling water provided in Table 1 is calculated from Equation 100 × m _ik / (m _i × T _s / 100), which is an average of two measurements.

Example additive pH Molar ratio of crosslinker / vinyl-OH % Insoluble fraction in boiling water Brookfield viscosity 2/50 mPas Brookfield viscosity 2/50 mPas after 4 weeks One 0.5pbwGABNa 20% 3.4 0.0018 28.6 366 535 2 2.5pbwGABNa 20% 3.4 0.009 93.8 322 528 3 5.0pbwGABNa 20% 3.4 0.018 93.9 299 532 C1 0.65 pbw glutaraldehyde 50% 3.4 0.018 94.9 394 Gel after 24 hours C2 No additives 3.4 0 0 364 448

Description: GABNa 20%: Aqueous solution of glutaraldehyde bis (sodium hydrogen sulfite) at 20% concentration

Example 4 and Comparative Example C3

Preparation of Premixes in the Form of Modified Polyvinyl Alcohol Granules

Partially hydrolyzed polyvinyl alcohol with a hydrolysis degree of 88 mol% and a viscosity of 18 mPa · s at 20 ° C in an aqueous solution of 4% concentration in a conventional commercial forced mixer equipped with a heating / cooling jacket (volume of 35 L). Charge 6 kg. Under jacket cooling the mixture is first stirred at a speed of 1200 rpm. The temperature rises slightly. When the temperature reaches 40 ° C. a solution of 240 g of glutaraldehyde in 960 g of water is added for 45 minutes. The temperature rises up to 49 ° C. It is then stirred at a rate of 600 rpm to cool the mixture to 40 ° C. The product is then collected and dried at 120 ° C. for 6 hours to a solids content of 99.6%. Microscopic image analysis indicates the presence of uniform granules free of the secondary component of the derivative.

Comparative Example C3

The same polyvinyl alcohol is mixed with glutaraldehyde bis (sodium hydrogen sulfite) without adding water. Microscopic image analysis revealed that it was a homogeneous mixture containing not only polyvinyl alcohol but also amorphous fine powder components.

The products of Example 4 and Comparative Example 3 are stored under the following conditions.

Climate 1: Open storage under laboratory climatic conditions with varying atmospheric humidity and temperature Climate 2: Store in dry atmosphere (on silica gel) at 25 ° C Climate 3: Store in a humid atmosphere (aqueous) at 25 ° C

Stored under each climatic condition and then assessed for visual appearance and manufacturability of aqueous solution at 10% concentration (90 ° C.). The results are summarized in Table 3 below.

keep Example Visual evaluation 10% concentration solution After 4 cycles 1 4 Granule invariant Clear solution After 4 cycles 1 C3 Product immutability Undissolved ingredients After 4 cycles 2 4 Granule invariant Clear solution After 4 cycles 2 C3 Product immutability Undissolved ingredients After 4 cycles 3 4 Slightly reduced fluidity due to moisture absorption Clear solution After 4 cycles 3 C3 Caking Undissolved ingredients 1 after 16 cycles 4 Product immutability Clear solution After 16 cycles 2 4 Product immutability Clear solution 3 after 16 cycles 4 Slightly reduced fluidity due to moisture absorption Clear solution

The novel polyvinyl alcohol compositions in the form of aqueous solutions are suitable for producing adhesives for wood-based substrates, such as wood, paper or cards, to produce paper laminates or spiral or parallel sleeves, in particular as waterproof adhesives for wood and paper. Do. From this aqueous solution, either alone or as a component of a laminate in a composite film, suitable as a waterproof packaging material with excellent barrier properties or suitable for use as a coating material for building materials, a pressure permeable separation membrane for separation of a battery membrane or an aqueous / organic mixture is prepared. The cast film for manufacturing can be manufactured. In addition to the above fields of use, it is used as a size for fabrics or glass fibers, binders for nonwoven compounds for producing reinforcing fibers, in particular for reinforcement of building materials, and as water vapor permeable sanitary napkin layers.

Claims (14)

Polyvinyl alcohol, a polyvinyl alcohol composition in the form of an aqueous solution comprising at least one polyaldehyde having at least 3 carbon atoms and completely masked as a water soluble hydrogen sulfite adduct and at least one compound acidic in water. The polyvinyl alcohol composition according to claim 1, wherein the degree of hydrolysis of the polyvinyl alcohol is 80 to 90 mol%. The polyvinyl alcohol composition according to claim 1, wherein the polyaldehyde is glutaraldehyde. The polyvinyl alcohol composition of claim 1 wherein the molar ratio of hydrogen sulfite to vinyl alcohol unit is (0.005 to 0.05): 1. The polyvinyl alcohol composition according to claim 1, wherein the acidic compound is a water-soluble salt of a polyvalent cation. The polyvinyl alcohol composition of claim 1, wherein the acidic compound can further form a complex compound with the polyvinyl alcohol. The polyvinyl alcohol composition according to claim 1, wherein the proportion of the acidic compound is 10 to 50% by weight based on the weight of the polyvinyl alcohol. Preparing an aqueous polyvinyl alcohol solution and A polyvinyl alcohol according to claim 1 comprising mixing an aqueous polyvinyl alcohol solution with at least 3 carbon atoms and at least one polyaldehyde completely masked as a water soluble hydrogen sulfite adduct and at least one acidic compound in water. Method of preparing the composition. Preparing an aqueous polyvinyl alcohol solution and The aqueous polyvinyl alcohol solution may contain at least one polyaldehyde having at least 3 carbon atoms or acetals thereof, at least a stoichiometric amount of alkali metal hydrogen sulfite, alkali metal disulfite or alkali metal pyrosulfite, and at least one compound acidic in water. A process for preparing a polyvinyl alcohol composition according to claim 1 comprising mixing with. Uniformly mixing at least partially water-soluble polyvinyl alcohol powder or granules with polyaldehyde completely masked as a hydrogen sulfite adduct to form a uniform solid water-soluble polyvinyl alcohol premix, Dissolving the polyvinyl alcohol premix in water and A process for preparing a polyvinyl alcohol composition according to claim 1 comprising the step of adding at least one acidic compound in water. A homogeneous, solid, water-soluble polyvinyl alcohol premix comprising at least three polyvinyl alcohols and at least one polyaldehyde that is completely masked as a water-soluble hydrogen sulfite adduct. Uniformly mixing the at least partially water-soluble polyvinyl alcohol granules with an aqueous polyaldehyde solution that is completely masked as a hydrogen sulfite adduct; and A process for preparing a homogeneous solid polyvinyl alcohol premix according to claim 11 comprising the step of subsequently drying the mixture. An adhesive comprising the polyvinyl alcohol composition according to claim 1. Cast film comprising the polyvinyl alcohol composition according to claim 1.